ATA5824-PLQW 80 Atmel, ATA5824-PLQW 80 Datasheet - Page 24

• Manufacturer Part Number: ATA5824-PLQW 80
• Manufacturer: Atmel

Specifications of ATA5824-PLQW 80

• Operating Temperature (min): -40C
• Operating Temperature (max): 105C
• Operating Temperature Classification: Industrial
• Product Depth (mm): 7mm
• Product Height (mm): 0.9mm
• Product Length (mm): 7mm
• Operating Supply Voltage (typ): 5V
• Lead Free Status / Rohs Status: Compliant

7.15
7.16
24
RX/TX Switch
Matching Network in TX Mode
ATA5823/ATA5824
The RX/TX switch decouples the LNA from the PA in TX mode, and directs the received power
to the LNA in RX mode. To do this, it has a low impedance to GND in TX mode and a high
impedance to GND in RX mode. The pin 38 (RX_TX2) must always be connected to GND in the
application. To design a proper RX/TX decoupling a linear simulation tool for radio frequency
design together with the measured device impedances of
page
values have to be found on board.
cuit of the switch. The principal switching operation is described here according to the
application of
.
Table 7-10.
Figure 7-13. Equivalent Circuit of the Switch
In TX mode the 20 mm long and 0.4 mm wide transmission line which is much shorter than /4 is
approximately switched in parallel to the capacitor C
C
antenna with pin RF_OUT, L
capacitor as discussed later). The transmission line can be approximated with a 16 nH inductor
in series with a 1.5 resistor, the closed switch can be approximated according to
with the series connection of 1.6 nH and 5 in this mode. To have a parallel resonant high
impedance circuit with little RF power going into it looking, from the loop antenna into the trans-
mission line a capacitor of about 7.6 pF to GND is needed at the beginning of the transmission
line (this capacitor is later absorbed into C
tion). To keep the 50 impedance in RX mode at the end of this transmission line C
also about 7.6 pF. This reduces the TX power by about 0.5 dB at 433.92 MHz compared to the
case where the LNA path is completely disconnected.
8
and C
22,
433.92
868.3
Frequency
315
Table 7-10 on page 24
9
has an impedance of about 50 looking from the transmission line into the loop
MHz
MHz
Figure 3-1 on page
MHz
Impedance of the RX/TX Switch RX_TX2 Shorted to GND
2
, C
and
10
Z(RX_TX1) TX mode
6. The application of
Figure 7-13 on page 24
, C
2.5 pF
Table 7-11 on page 25
(4.8 + j3.2)
(4.5 + j4.3)
8
11
(5 + j9)
and C
9
RX_TX1
, which is then higher as needed for 50 transforma-
1.6 nH
9
connected (using a C
TX
9
to GND. The antenna connection between
Figure 4-1 on page 7
5
shows an approximate equivalent cir-
Table 7-1 on page
should be used. The exact element
Z(RX_TX1) RX mode
9
without the added 7.6 pF
(11.3 – j214)
(10.3 – j153)
(8.9 – j73)
works similarly.
11,
4829D–RKE–06/06
Table 7-7 on
Table 7-10
7
has to be